Just download the full installer & install it, you won't lose anything. You can always install new version without losing anything you just can't downgrade without clean install.
Beware though that I upgraded from PB6 to Final Version & now the widgets are not appearing & Social Share isn't even working, but everything else is fine. It's been reported about the widget bug already by many people.
There is no upgrade; just stay on PB6 and remove the Feedback icon from your dock.
Or, if you're bored and have time to kill, download and run the full installer which will do nothing apart from change a release number (from 388b to 389).